Download common protocol for distributed network file system

Common protocol for disributed network file sysytem
231
COMMON PROTOCOL FOR DISTRIBUTED NETWORK FILE SYSTEM
P. Peniak 1) , F., Kallay2)
1),
IT service center for Easter Europe (SCEE) Continental AG, Continental Matador Truck Tires s.r.o
T.Vansovej 1054/45, 020 01 Púchov, tel.: +421 42 4613479,e- mail: [email protected]
2),
Faculty of Electrical Engineering, University of Žilina,
Univerzitná 8251/1, 010 26 Žilina, e- mail:[email protected]
Summary Paper deals with common protocol for distributed network file system. Focus is on CIFS protocol from Microsoft,
the enhanced version of Microsoft Server Message Block (SMB), that is proposed as possible common solution
for file sharing among distributed systems. There are new requirements included as well, that are to be
implemented due to recent changes in applications and devices and has been addressed in new generation of
distributed file system protocols such as AFS2, CODA and WebDAV.
1. INTRODUCTION
A network file system is defined as any
computer file system that supports sharing of files,
printers over a computer network. Network file
services enable computers attached to the network to
access files stored on other computers in the same
way that they access files on their own disks. That
is, the client interface used by programs should not
distinguish between local and remote files. It is up to
the network file system to locate the files and to
arrange for the transport of the data [1], [2].
The computer which provides access to its files
and directories is called file server, and the computer
using these files and directories is the client. A
computer can be client and server at the same time.
For communication between servers and clients, the
specific network protocols are used. The most
popular are the following protocols, see Tab.1:
SMB (SAMBA implementation of SMB server in
LINUX) so users who work with UNIX or Microsoft
operation systems, are able to use the both network
file systems. Another option is to develop and
implement a common network file system that
would be supported by all platforms and suppliers.
Then, just one protocol stack could be used for
access and sharing files via Internat. This option is
shown in Fig.1c.
a)
b)
Tab.1 Network file system protocols
–
7
6
5
4
3
Novell
NetWare
NCP
DoD
TCP/IP
FTP, HTTP, NFS
SPX
IPX
TCP/UDP
IP
Microsoft Network
SMB, RPC
NetBIOS
NetBEUI
NFS(Network File System) –SunSystems, IETF
NCP (NetWare Core Protocol) -Novell
Server Message Block (SMB) –IBM, Microsoft
File Transfer Protocol (FTP) -IETF
Hypertext Transfer Protocol (HTTP) -IETF
These protocols were implemented in the
different operation systems such as Microsoft
Windows (SMB) and UNIX/LINUX (NFS) [3].
Therefore, their clients cannot use the different
network fileservers by default, as shown in Fig.1a).
There are multi-client solutions applied, with several
implemented network file system protocols within
given operation system. Fig.1b) shows multiclient
configuration, with the protocol stacks for NFS and
c)
Fig.1 Possible access to network file systems
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Advances in Electrical and Electronic Engineering
Due to Microsoft superiority in number of installed
nodes in Internet, the introduction of common
network file system protocol will require its strong
support and acceptance. Microsoft is currently trying
to establish its protocols as the official standard of
the Internet. It could perspective replace the
currently used FTP protocols and file transfers
through the HTTP protocol, which represents
substantially heterogeneous environment with
problematic security. Microsoft has been trying to
push Common Internet File System (CIFS),
protocol through standardization process since 1996
[4]. CIFS drafts were even provided to IETF so that
it could be approved among Internet stadard
protocols.
Support of basic file operations (open, close,
read, write and seek).
Record lock and unlocking for multiple clients
access and file sharing and locking.
Performance and portability
Highly integrated within the operating system.
Support for all recent Microsoft platforms and
other operation systems such as Unix, VMS,
IBM, Macintosh
Security
Support of anonymous access(no authorization).
Enhanced security and authenticated access
Optimization
Improved protocol performance
Reduction of overhead in SMB protocol
Global File Names
No need to mount remote file systems,
Access based on globally significant names
Unicode File Names
2. COMMON INTERNET FILE SYSTEMS
Common Internet File Systems (CIFS) is the
enhanced version of Microsoft Server Message
Block (SMB) protocol that defines a remote fileaccess to share data on local disks and network file
servers, among distributed systems across intranets
and the Internet. In addition to SMB, which was
developed on the top of NETBIOS-API, CIFS is
able to run over TCP/IP and utilizes the Domain
Naming Service (DNS). It is optimized to support
communication via Internet with various speed
levels. CIFS complements Hypertext Transfer
Protocol (HTTP) while providing more sophisticated
file sharing than traditional protocols, such as FTP.
The CIFS protocol is not only available for
servers and PCs, but also for embedded devices and
distributed systems. It had to be scaled down in size
and reworked for multitasking features to meet the
needs of embedded devices such as real-time,
deterministic response times, small memory, and a
variety of microprocessor–file system combinations.
The using of CIFS for servers and embedded devices
is shown in Fig.2. The file sharing is independent
on hosting platform and embedded operation
system/file system.
Because CIFS is mainly based on SMB protocol we
will explain below its core functions.
3. SMB PROTOCOL
The SMB (Server Message Block) protocol
was originally developed by the company IBM in
co-operation with the company Microsoft for one of
the first network operating systems, the PC Network
Program v.1.0. Today, this protocol is the most
frequently used one in the field of peer-to-peer
communication of LAN network file servers and
clients. The SMB protocol is currently used by file
and print servers IBM, Microsoft’s network
operating systems (Lan Manager, Windows NT, XP,
Vista). The protocol header and basic services are
shown in Tab. 2 and Tab. 3.
Tab. 2 Header of SMB protocol
SI D
S
C R
C
A
H
RC
RS
NI
D
PI
D
UID
MI
D
P
PC
d
BL
B
1
3
1 1
1
2
15
2
2
2
2
1
2
2
1
Σ 38 B
MARKING
RC
Identification of SMB server’s dialect
Functional code of called SMB service
SMB function return code class
Result of operation in register of AH
processor
Return code of operation
RS
NID
PID
UID
Reserve
Net Path ID
Process ID
User ID
Reserve for future extension
Identifier allocated to shared means
Identifier of client’s process
Identifier of user
MID
Prmct
Multiplex ID
Parameter
Count
Multiplex identifier of client process
Number of optional parameters for called
function
S
C
R
AH
Fig. 2 CIFS protocol in servers and embedded devices
CIFS provides the following functions:
File Access
MEANING
SMB
Identificatio
n
Server
Command
Return Class
Processor
AH register
Return Code
SID
Identification of SMB protocol (0xFF)
Common protocol for disributed network file sysytem
PC
BL
B
Parameter
Code
Buffer
Length
Buffer
Called function parameter code
Length of data part of SMB block
First octet of data part of SMB block
Tab.3 Example of SMB services
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The protocol works on the basis of the client/server
model. A server provides to network clients the cocalled shared resources, usually shared disks,
directories, print files and named pipes. Shared
resources are identified through an universal
network address called UNC
\\server_name \resource_name.
SMB BLOCK
SERVICE
CODE
SMB_COM_CREATE_DIRECTORY
SMB_COM_DELETE_DIRECTORY
SMB_COM_OPEN
SMB_COM_CREATE
SMB_COM_CLOSE
SMB_COM_DELETE
SMB_COM_RENAME
SMB_COM_READ
0x00
0x01
0x02
0x03
0x04
0x06
0x07
0x0A
SMB_COM_WRITE
0x0B
SMB_COM_LOCK_BYTE_RANGE
0x0C
SMB_COM_UNLOCK_BYTE_RANGE
0x0D
SMB_COM_CHECK_DIRECTORY
0x10
SMB_COM_SEEK
SMB_COM_TREE_CONNECT
0x12
0x70
SMB_COM_TREE_DISCONNECT
0x71
SMB_COM_NEGOTIATE
0x72
SMB_COM_SESSION_SETUP_ANDX
0x73
SMB_COM_LOGOFF_ANDX
0x74
SMB_COM_OPEN_PRINT_FILE
SMB_COM_WRITE_PRINT_FILE
SMB_COM_CLOSE_PRINT_FILE
0xC0
0xC1
0xC2
Creation of directory
Deletion of directory
Opening of file
Creation of directory
Clos ing opened file
Deletion of file
Renaming of file
Reading from an
opened file
Writing into opened
file
Locking file byte
range
Unlocking file byte
range
Searching through
directory
Transfer in open file
Connection to shared
means
Disconnection from
shared means
Negotiation of SMB
parameters
Connection to SMB
server
Disconnection from
SMB server
Opening print file
Writing to print file
Clos ing print file
The SMB block with a client’s request and a
server’s answer are practically identical, they just
differ in the data part and the length of the data
buffer. An example of communication of a client
with an SMB server can be seen in Fig. 3.
SMB_COM_NEGOTIATE
NID:0,UID:0,PID:53
SMB_COM_SETUP
NID:0,UID:1,PID:53
SMB
client
SMB_COM_TREE_CONNECT
NID:10,UID:1,PID:53
SMB
server
SMB_COM_CREATE_DIRECTORY
NID:10,UID:1,PID:53,FID:1 „\x“
SMB_COM_TREE_DISCONECT
NID:100,UID:1,PID:53
1029
SMB_COM_TREE_DISCONECT
NID:0,UID:0,PID:53
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Fig.3 Example of client communication with SMB server
A client secures the formulation of requirements of
shared server resources. The SMB server analyses
requirements sent by a client in the form of an SMB
block (packet), it checks an access permission, and
based on that it carries out a required operation (file
opening, writing into print file, creation of a
directory, etc.) The reply, together with the result, is
sent to the client in an identical SMB block. In the
implementation of SMB servers, two different
methods of securing access to shared means of the
server are offered through:
control of access at the share level
control of access at the user level
In the first case the access to shared resources
is allowed to all network nodes that have a valid
password allocated to a resource of a server. During
an attempt to access any server resource, a password
is required from the client.
After its successful entering, an NID
(Network ID) resource identifier is allocated to the
client, through which it accesses the resource. Thus
a number of passwords with different access levels
can be allocated to each shared server resource. In
the other case, the client is verified though a name
and a password immediately after the connection to
the server, and in the event of their correctness, the
server allocates to the client its user identifier UID
(User ID), through which the server derives access
rights to individual shared resources. In a multi-user
environment, when several processes can
communicate simultaneously with the server, a
couple of PID (Process ID) and MID (Multiple ID)
identifiers can serve for their distinguishing.
The
client
sends
the
server
an
SMB_COM_NEGOTIATE request, through which
the server and the client negotiate connection
parameters and a supported protocol version.
Subsequently, the client sends to the server a
SMB_COM_SETUP request, in which there is the
user’s name and password. If the server works in the
user-level mode, it allocates an UID identifier to the
client. Through the SMB_TREE_CONNECT
message the client connects to a shared directory
with a TID identifier allocated by the server. Then
the creation of a (\x) FID subdirectory and the
disconnection of the server follows.
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Advances in Electrical and Electronic Engineering
Fig.3: Example of SMB packet
4. CONCLUSION
Traditional network file systems were created in
a world where the dominant network paradigm was
the LAN/WAN. Lack of standardization caused that
common standard has not been selected and
approved yet, despite to ISO standard FTAM (File
Transfer and Access Protocol) and recent Microsoft
activities with its proposed solution -CIFS.
In addition the network file system challenge has
become the distributed file system and connections
via Internet/WAN, as there is move from selfcontained LAN environments to a world of
distributed system and even rarely connected
devices. This kind of network environment
introduces at least three main challenges:
Authentication
Data Transport
Synchronization
Some of these issues could be solved at the
application level rather than the file system level.
For instance, Rsync, a powerful program that came
out of the Samba project provides remote file
synchronization over the network. Another
alternative to traditional protocol is for example,
AFS (Andrew File System) and CODA. Coda is
a distributed file system developed from AFS2.
Coda is designed for mobile computing in an
occasionally connected environment. Coda clients
maintain a persistent cache of copies of files from
the server. Coda checks the network both for the
availability of connections between client and
server, and for the approximate bandwidth of the
connection.
As explained there are still the different solutions in
place, such as NFS in Unix and CIFS/SMB in
Microsoft world. The future development must
consider not only requirement for common file
system and protocol, but also to include the new
requirements
regarding distributed
systems,
replications, caching, which have not been taken into
consideration yet.
Therefore the next development will have to
solve the mentioned challanges and to come with a
proposal for new solution, which will enable
implementation of distributed file system for open
and embedded systems as well.
REFERENCES
[1] FRANEKOVÁ, M., KÁLLAY, F., PENIAK, P.
VESTENICKÝ, P.: Komunika ná bezpe nos
priemyselných sietí. ŽU Žilina, 2007, ISBN
978-80-8070-715-6.
[2] KÁLLAY, F., PENIAK, P.: Po íta ové sit
LAN/MAN/WAN a jejich aplikace, Grada,
2003, ISBN 80-247-0545-1.
[3] PUŽMANOVÁ, R.: Moderní komunika ní sít
os A do Z, Computer press 2002, ISBN 807226-098-7.
[4] firm documentation